Engines have provided an invaluable service to mankind by performing work at a rate that is many times what man can do. Over about 200 years, piston engines have evolved into quite sophisticated devices for converting heat energy into motive force. Steam engines were developed first. Here heat is provided to an external boiler to produce a reservoir of hot steam. The steam is admitted into a cylinder with a movable piston, which then moves, consuming energy from the steam and exerting force on a crankshaft. Later, internal combustion engines were developed. These engines take in air and mix it with a fuel. The fuel/air mixture is ignited in a cylinder with a movable piston to provide hot combustion gases that exert a force on the piston, which in most engines is coupled to and drives a crankshaft. Internal combustion engines, in particular, are relied upon for a wide variety of applications, inasmuch as they are in many ways more convenient than their steam counterparts, especially for mobile applications where high power to weight ratios are necessary. There are two types of engines, which are classified by their cycles.
Two-stroke cycle engines tend to be high power, high speed, and simple, but dirty and inefficient. They have high power for their size, inasmuch as the power stroke occurs twice as often for any given speed of crankshaft rotation, compared to four-stroke cycle engines. Two-stroke engines tend to be dirty and inefficient because intake and exhaust are not accomplished by separate strokes but rather are accomplished by slot(s) in the bottom the cylinder which allow the exhaust gases to leave and fresh air and fuel to be inducted. Since this is done in a very short amount of time, exchange of the gases is incomplete, leading to inefficiency. Further, although there are other methods of lubrication, most 2-stroke engines are lubricated by addition of the lubricating oil to the fuel itself. The oil is, therefore, also burned in an inefficient pollution-creating manner.
Four-stroke cycle engines are by far the most commonly used engines. They have separate intake and exhaust strokes as well as a power stroke and a compression stroke. The separation of intake and exhaust ensures intake of sufficient air to complete combustion of the fuel and almost complete exhausting of combustion products. However, the power strokes only occur once in each four piston strokes, as compared to once in every two stokes in two-stroke cycle engines, so the power is less for the same size and speed of the engine. While the four-stroke engine runs cleaner and consumes fuel more efficiently, other things occur that make a four-stroke engine run with about the same net efficiency as a two-stroke engine. For one thing, in a four-stroke cycle engine, energy is consumed in the intake and exhaust stroke as well as the compression stroke. (The exhaust stroke uses energy, but it is small compared to that used in the intake and compression strokes.)
The two major types of four-stroke cycle engines, the Otto cycle and the Diesel cycle, differ only in how the ignition of the fuel is accomplished, the compression ratios and the method of delivering fuel to the cylinders. The energy and power considerations remain the same.
It is well known from thermodynamic laws that there is a direct correlation between the maximum available efficiency of an engine verses its compression ratio. The diesel engine has the advantage in efficiency with its higher compression ratio. For this discussion, however, the more general term "expansion ratio" will be used, since this is actually what produces power and determines efficiency. Furthermore, since the present invention has no compression stroke, as described below, the notion of a compression ratio is not applicable.
The (ideal) work available from a fixed amount (in this case one mole) of gas at a given temperature T (in degrees Kelvin) expanded in volume at an initial pressure P1 to a final pressure P2 is given by Equation 1. EQU W=RTln(P1/P2) (1)
The units chosen for R, the universal gas constant, determine the units that the energy is expressed in. If Joules are desired, then R=8.314. One uses ideal equations, inasmuch as that gives a maximum obtainable, and it is correct to compare maximums to see if a potential improvement is obtainable. In a real engine many other variables come into play. One important factor, in particular, is the ratio of the specific heat at constant temperature and constant pressure of the gases in the cylinder. However, these gases are dictated by the choice of fuel and therefore are not a variable for an engine cycle according to the present invention. The equivalence ratio is a variable and can effect the Cp/Ct ratio. That is discussed below.
For any given temperature, the ratio of the beginning and ending pressures (which is the expansion ratio) determines how much energy can be extracted. In a conventional two- or four stroke cycle engine, equation (1) also calculates the amount of energy required to compress the gases during the compression stroke. If T were constant one would not expect to extract any energy from such a system. The reason net energy is extracted is that T for combustion during the power stroke is much higher than T for the compression stroke. The intake and exhaust strokes consume much less energy since the chamber is open to the atmosphere and the pressure differentials (P1/P2) are much smaller.